The intersection of the Hollywood and Pasadena Freeways, known as the Four Level Interchange, is one of the major landmarks in Los Angeles and a symbol of the city's post-World War II development.

SR 170 begins its northbound route at the junction with the Ventura Freeway, continuing the freeway northwards. US 101 leaves the freeway, merging onto the Ventura Freeway and heads west. SR 134 continues the Ventura Freeway, heading east. On the southbound side, a sign indicates "END Route 170." Curiously, there is no interchange from SR 134 West to US 101 South. This connector route was put on hold pending the construction of the Laurel Canyon Freeway, which never came to fruition. Motorists intending to go in that direction must exit SR 134 at Cahuenga Boulevard, make a left, continue on Lankershim Blvd. and follow the signs near Universal Studios to re-enter on US 101. Likewise, there is no interchange from US 101 North to SR 134 East. Motorists intending to go in that direction must exit US 101 at Vineland Ave., make a right, make another right on Riverside Dr. and enter SR 134 on the left. This interchange is also known as the "Hollywood Split."

SR 170 then continues through the northeastern portion of the San Fernando Valley, finally merging onto northbound I-5. There is no connector route to I-5 South because the angle between the two freeways is too acute.

There are HOV lanes in operation 24 hours a day in each direction of SR-170 between I-5 and the Hollywood Split interchange. There is a direct connection from the northbound SR-170 HOV lanes onto the northbound I-5 HOV lanes, as well as from the southbound I-5 HOV lanes onto the southbound SR-170 HOV lanes. This makes it possible to connect with the I-5 HOV lanes as well as the SR-14 HOV lanes (from the I-5) without merging into regular lanes.

Plans for the Hollywood Freeway officially began in 1924 when Los Angeles voters approved a "stop-free express highway" between Downtown Los Angeles and the San Fernando Valley.[1] The first segment of the Hollywood Freeway built was a one and a half mile stretch through the Cahuenga Pass. That segment opened on June 15, 1940. It was then known as the "Cahuenga Pass Freeway." Pacific Electric Railway trolleys ran down the center of this freeway until 1952. The next section of the freeway that stretched from the San Fernando Valley to Downtown Los Angeles opened on April 16, 1954 at a cost of $55 million. The final section, north of the Ventura Freeway to the Golden State Freeway was completed in 1968.[1]

Hollywood freeway through the Cahuenga Pass in 1972

A year after the Hollywood Freeway opened, it was used by an average of 183,000 vehicles a day, almost double the capacity it was designed to carry. Actor Bob Hope called it the "biggest parking lot in the world" in his routine.[1]

The segment through Hollywood was the first to be built through a heavily populated area and requiring the moving or demolition of many buildings, including Rudolph Valentino's former home in Whitley Heights. The freeway was also designed to curve around KTTV Studios and Hollywood Presbyterian Church.[1] Much of the rubble and debris from the buildings removed for the freeway's construction was dumped into Chávez Ravine, the current home to Dodger Stadium.[1]

In 1967, the Hollywood Freeway was the first freeway in California that had ramp meters.[1]

Near the Vermont Avenue exit, there's a seemingly over-wide center strip now filled with trees. This is where the never-built Beverly Hills Freeway was to merge with the Hollywood Freeway. Plans for the Beverly Hills Freeway were halted in the 1970s.[5]

Hollywood Freeway at night with Downtown L.A. in the background.

The Hollywood Freeway is an expansion of the original Cahuenga Parkway, a short six-lane freeway that ran through the Cahuenga Pass between Hollywood and Studio City. The Cahuenga Parkway featured Pacific Electric Railway "Red Car" tracks in its median, but by the 1950s these tracks were out of service due to radical reductions in Red Car service. The Pacific Electric right-of-way later accommodated an additional lane in each direction.

The second location of Los Angeles High School was in the path of the freeway. The school moved to its third and current location in 1917. The school buildings were converted into a school for boys with truancy problems until 1948, when it was demolished to make way for the freeway.[6]

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see the list of postmile definitions).[8] Segments that remain unconstructed or have been relinquished to local control may be omitted. The entire route is in Los Angeles, Los Angeles County.